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UNIT 2: The Biology of Behavior Structure of a (typical) Neuron dendrites soma myelin sheath synapses axon terminal buttons The Neural Impulse Neural impulse – a brief electric surge that carries the neuron’s message All-or-None Law – like a gun, a neuron either fires or it doesn’t, and it’s impulses are all the same size (a weaker stimulus will not create a smaller impulse) Synapse – when an impulse reaches its terminal buttons, it triggers the release of chemical messengers (neurotransmitters). The chemicals move across to be received by the receiving cell (muscle, gland, or another neuron) David Suzuki - Neural Impulse & Synapses Typical Synapse Copyright © Allyn & Bacon 2007 Otto Lowei (1921) “Vagusstoff” (actually Acetylcholine) Neurotransmitters Neurotransmitters – Chemical messengers that relay neural messages across the synapse They can be excitatory (increase likelihood that following neurons will fire) or inhibitory (decrease likelihood that following neurons will fire) They play a key role in everything from muscle movements to moods and mental health some 15-20 chemical substances act as neurotransmitters, each one a specific size/shape to bind with a particular location Five Important Neurotransmitters Dopamine Serotonin Norepinephrine Acetylcholine Endorphins Neurotransmitters Serotonin Normal Function: Regulates sleep and dreaming, mood, pain, aggression, appetite and sexual behavior Problems with Imbalance: Depression, certain anxiety disorders, obsessivecompulsive disorder Substances that Affect: Prozac, hallucinogenics (e.g. LSD) Neurotransmitters Normal Function: Norepinephrine Controls heart rate, sleep, sexual responsiveness, stress, vigilance and appetite Problems with Imbalance: High blood pressure, depression Substances that Affect: Tricyclic antidepressants, beta blockers Neurotransmitters Normal Function: Dopamine Produces sensations of pleasure and reward; used by CNS neurons in voluntary movement Problems with Imbalance: Schizophrenia, Parkinson’s disease Substances that Affect: Cocaine, amphetamines, Ritalin, alcohol COCAINE EFFECTS Neurotransmitters Acetylcholine Normal Function: Primary transmitter used by neurons carrying messages from CNS; involved in some kinds of learning and memory Problems with Imbalance: Certain muscular disorders, Alzheimer’s disease Substances that Affect: Nicotine, botulism toxin, curare, atropine Neurotransmitters Endorphins Normal Function: Pleasurable sensations and control of pain Problems with Imbalance: Lowered levels resulting from opiate addiction Substances that Affect: Opiates: opium, heroin, morphine, methadone Review Nervous System Component dendrite Metaphor neuron axon terminal button Like the insulation that covers electrical wires myelin sheath like a tree. Also, each branch is a telephone wire that carries incoming messages to you synapse Like a silicon chip in a computer which receives and transmits information Like an electrical cable that carries information Like the nozzle at the end of a hose, from which water is squirted Like a railroad junction, where two trains may meet
